Filter apparatus are known for filtering particles in a fluid stream. The filtration operation essentially removes particles of a particular size from the fluid stream to cleanse the fluid stream of contaminants.
As the fluid flows through the filter apparatus, certain fluids such as hydraulic fluids and diesel and gasoline fuels can have resistance to the conductance of electricity. As such, a static charge can build up within the fluid from the action of the fluid flowing through the non-metallic piping and filter media. With some of the more advanced compositions of filter media, and with the increasing acceptance of synthetic and biodegradable fluids with low conductivity values (i.e., little or no metal additives), static charge can accumulate within the filter apparatus. When the potential between the fluid and a conductive housing component reaches a certain level, a spark can jump to a surface of the housing component. This can be undesirable in many situations.
One technique for removing the static charge in the fluid is to add an anti-static agent such as DuPont Stadis 450 to make the fluid slightly conductive. However, anti-static agents can lose potency over time and will typically have to be re-added (re-doped) to the fluid at regular intervals.
Certain filter apparatus are also known which attempt to remove static charge as fluid flows through the filter apparatus. For example, Patent Specification U.S. Pat. No. 3,933,643 to Colvin, et al., discloses a technique to remove static charge in filters for a flammable liquid or gas wherein nonconductive fibrous filter elements are treated with resins containing finely divided carbon. The treated fibers are then fabricated into filter elements which are electrically connected to metal end caps using a conductive sealing composition. The metal end caps are then electrically connected to ground. The static charge in the liquid or gas passing through the filter element is drawn off through the ground path. Patent Specification EP-A-0402657 and Patent Specification DE-C3325526 also show what appears to be conductive adhesive disposed between the end of filter media and an end cap.
Patent Specification U.S. Pat. No. 3,186,551 to Dornauf, shows a similar technique wherein a pair of conductive inner and outer perforated metal tubes surround the filter media, while a conductive wire helix is included within the filter media. The wire helix and metal tubes are electrically connected to metal disk members at either end of the filter element and then to metal annular members. One metal annular member is in direct mechanical contact with a central spindle which contacts a metal partitioning wall of the filter housing, while the other annular member is in direct mechanical contact with the metal partitioning wall.
Patent Specification U.S. Pat. No. 4,999,108 to Koch, et al., shows a similar technique where a wire electrically connects a perforated metal support tube intermediate the filter media with a metal fastening screw. The metal fastening screw is then grounded by direct mechanical contact with a metal fastening spider (housing).
Still another technique for grounding components within a filter apparatus is shown in Patent Specification U.S. Pat. No. 4,187,179 to Harms, wherein spring fingers are in direct mechanical contact with and electrically connect a metal support plate to a lid of the filter container.
Patent Specification WO-A-92/04097 shows a technique where the outer housing is formed from conductive material and attached to ground to dissipate charges generated by fuel passing through the filter media.
Patent Specification WO-A-87/01301 shows conductive filter media material electrically connected through conductive adhesive to a conductive end cap. The end cap is then attached by a conductor to ground.
While the above types of filter apparatus might be useful in certain situations, the applicants believe that the known filter apparatus can require special housing structures for the filter elements or additional parts such as spring fingers or spindles; require tight tolerances and/or intimate mechanical contact between the filter element and the housing; and can be difficult and time-consuming to assemble such that a proper ground path is provided and maintained between the filter element and the housing. Applicants believe that heretofore there has not been a filter apparatus which removes static charge from fluid and which (i) does not require any special housing structure other than what would normally be found with nonconductive filter apparatus, and (ii) is easy to assemble so as to provide and maintain a proper ground path between the filter element and the housing.
As such, applicants believe there is a demand for a new and improved filter element which addresses the above drawbacks.